A light emitting diode converts electric energy into light energy. The light emitting diode can implement various colors by controlling a composition ratio of compound semiconductor.
The light emitting diode emits energy corresponding to an energy gap between a conduction band and a valance band by a combination of electrons of an n layer and holes of a p layer when a forward voltage is applied to the light emitting diode. The energy is mainly emitted in a heat or light form. In the case of the light emitting diode, the energy is emitted in the light form.
For example, nitride semiconductor has high thermal stability and wide band gap energy. As a result, the nitride semiconductor has received much attention in development fields of optical devices and high output electronic devices. In particular, a blue light emitting diode, a green light emitting diode, an ultraviolet (UV) light emitting diode, and the like using the nitride semiconductor have been widely commercialized.
The existing nitride semiconductor has a problem of non-uniformity of current injection, low heat emission efficiency, low light emission efficiency, etc. Therefore, to use the light emitting diode including the nitride semiconductor as a high efficiency light source, the technical development for maximum internal quantum efficiency, high transparent ohmic electrode, and improvement in light extraction is very important. Recently, many studies have been conducted on improvement in external quantum efficiency by improving the light extraction efficiency rather than on improvement in the external quantum efficiency by improving the internal quantum efficiency.